A publication entitled: Flame rig testing of thermal barrier coatings and correlation with engine results by G. Johner and K. K. Schweitzer discloses metal structural components provided with heat insulating protective layers of zirconium dioxide. A disadvantage of zirconium dioxide protective layers is seen in that due to the high density of zirconium dioxide and due to the required thickness of the layers, the total weight of the protected metal structural components is substantially increased by the protective layers. Further, in order to achieve the required thickness of the protective coating, several plasma sprayed layers must be applied, which results in high operational temperatures corresponding to those occurring in gas turbine power plants. These temperatures applied during the manufacturing phase lead to substantial material stress between the protective layers relative to one another and between the protective coating and the base material of which the metal structural component is made. As a result, the protective coating has a tendency to chip off layer by layer.
U.S. Pat. No. 5,006,419 (Grunke et al.) which is partially based on German Pat. Publication 3,906,187, discloses a titanium alloy structural component provided with a titanium fire inhibiting protective coating of aluminum. The protection mechanism which is achieved by the evaporation of aluminum has the drawback that the aluminum protective coating is used up in a rather non-uniform manner. As a result, it is possible that the protective coating has been locally eaten away completely while other areas are still properly protected against thermal loading. However, unprotected local areas of the structural component that requires protection against thermal loading, involve the danger of a restructuring of the microstructure by recrystallization near the surface or an ignition of the base material of which the metal structure compound is made, such as titanium alloy. A recrystallization or microrestructuring of the surface layer of the metal structural component due to local overheating results in a reduced material strength of the structural components. Thus, there is still room for improvement. U.S. Pat. No. 4,935,193 (Grunke et al.) discloses an improved coating of an aluminum niobium combination on the surface of a structural component of titanium or titanium alloys for protecting the component against oxidation.